1. Field of the Invention
The present invention relates to an induction-heating fixing apparatus and an image forming apparatus having the induction-heating fixing apparatus such as a copying machine, printer, or facsimile, particularly to power-distribution control of an induction-heating fixing apparatus using an induction-heating system.
2. Description of Related Art
An image forming apparatus is provided with a fixing apparatus for fixing a toner image on a recording material by heating the toner image. An induction-heating fixing apparatus using an induction-heating system has is provided with a heating member in which an induction-heating coil is set as a heating source and a pressuring member for forming a nip portion by pressure-contacting with the heating member. The heating member uses a heating roller or a heating belt, and a mold release layer is formed on the surface of a conductive base substance.
The induction-heating coil is wound into a length corresponding to the maximum passing-sheet width of a recording material, which must heat the entire region of a heating roller wider than the maximum passing-sheet width at the time of warm-up or standby. Moreover, when passing a recording material having a width smaller than the maximum passing-sheet width, there is a problem that the temperature of the no-passing-sheet portion of a heating roller rises. To solve the problem, a conventional method of dividing an induction-heating coil into a plurality of coils and arranging the coils is disclosed.
For example, a method of controlling the temperature of an induction-heating roller for controlling a current or voltage to be supplied to each of the divided plurality of induction-heating coils in accordance with an output of a temperature sensor in order to shorten the rise time for raising a heating roller up to a fixable temperature and obtain the uniformity and temporal stability of set temperatures of various portions of the roller is disclosed (JP-Tokukaisho-57-128373A).
Moreover, a high-frequency heating fixing method of dividing a coil into a plurality of coils and winding the coils on an iron core so as not to raise the temperature of the no-passing-sheet portion of a fixing member, selecting a coil for passing a current in accordance with the size of a toner-image support body (recording material), and changing induction-heating regions, is disclosed (JP-Tokukaisho-58-178385A).
Like the above-described prior art, when the driving-control of supply currents is performed independently with respect to each of a plurality of induction-heating coils which is divided and arranged, induction-heating coils can be simultaneously driven or not simultaneously driven in accordance with a change of operation modes or passing-sheet sizes of an image forming apparatus.
When a high-frequency current flows through an induction-heating coil constituted by a copper wire, the coil is influenced by a magnetic field to cause minute vibrations. When a characteristic such as an inductance or capacitor capacitance of an induction-heating coil or heating roller differs, the frequency of a current supplied from a power supply becomes a different frequency. Because of such factor, when adjacent induction-heating coils are simultaneously driven, currents of different frequencies flow through the adjacent induction-heating coils, thereby minute vibrations are generated, and large vibrations are generated due to overlap of the minute vibrations. Moreover, there are problems that a heating roller and the like are resonated due to the vibrations and noises such as resonant sounds are generated.
However, when each of the induction-heating coils is not driven along with each other, the temperature of a heating member may be lowered due to the loss time when the heating member is not heated by the induction-heating coil. The temperature drop causes a fixing trouble, causes the temperature rise speed of the heating member to lower, and a trouble occurs that a warm-up time WUT (time until the heating member reaches a fixable temperature) is increased. Therefore, it is requested to perform power distribution control to each induction-heating coil with no loss time when the heating material is heated.
However, because a maximum rated current (e.g. 15[A]) is set to an image forming apparatus, a maximum current usable for a fixing apparatus is restricted in accordance with operation modes of apparatus portions other than a fixing apparatus such as image forming mode, warm-up mode, or standby mode.
Therefore, for the power distribution control of a fixing apparatus, it is requested to avoid induction-heating coils from being simultaneously driven, and to perform finer control by corresponding to operation modes of apparatus portions other than the fixing apparatus in an image forming apparatus and by considering the current supply balance between the induction-heating coils.